Horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope image of Sagittarius A ∗

Abstract

Horizon-scale images of black holes (BHs) and their shadows have opened an unprecedented window onto tests of gravity and fundamental physics in the strong-field regime. We consider a wide range of well-motivated deviations from classical General Relativity (GR) BH solutions, and constrain them using the Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), connecting the size of the bright ring of emission to that of the underlying BH shadow and exploiting high-precision measurements of Sgr A*’s mass-to-distance ratio. The scenarios we consider, and whose fundamental parameters we constrain, include various regular BHs, string-inspired space-times, violations of the no-hair theorem driven by additional fields, alternative theories of gravity, novel fundamental physics frameworks, and BH mimickers including well-motivated wormhole and naked singularity space-times. We demonstrate that the EHT image of Sgr A* places particularly stringent constraints on models predicting a shadow size larger than that of a Schwarzschild BH of a given mass, with the resulting limits in some cases surpassing cosmological ones. Our results are among the first tests of fundamental physics from the shadow of Sgr A* and, while the latter appears to be in excellent agreement with the predictions of GR, we have shown that a number of well-motivated alternative scenarios, including BH mimickers, are far from being ruled out at present.

Analyzing the H0 tension in F(R) gravity models

“…Moreover, other open windows to check the possible existence of axion fields as dark matter candidates might lie on the effects that may be induced on the black holes' shadows when considering them surrounding by this type of dark matter, a very active and current field nowadays [48].…”

Constraints on charged symmergent black hole from shadow and lensing

“…In fact, the highest recorded observational bound on the electric charge of Sgr A* is ∼ 3 × 10 8 C (or ∼ 9.16 × 10 −9 m in geometrized units). Apart from the charge, one notes that exclusion of M87* spin parameter a in the present study is justified by the analyses of [51].…”

“…from the SMBH (in kpc) is also given. In addition to these data, we obtain the allowed 1σ− bands for the Schwarzschild deviation [34,35,51,121], which read 4.55M ≤ R sh ≤ 5.22M , and 4.31M ≤ R sh ≤ 6.08M for Sgr. A* and M87*, respectively.…”

Toward General Relativistic Magnetohydrodynamics Simulations in Stationary Nonvacuum Spacetimes

“…Careful explorations of these spacetimes, especially with a focus on the physicality of the underlying matter (e.g., how well energy conditions are satisfied), is left for future work. Vagnozzi et al (2023) gave an immense compilation of spacetime metrics, including those corresponding to static and spherically symmetric spacetimes. These metric functions describe alternative nonspinning BHs, which are of considerable interest and can be studied using simulations.…”

“…It has also been possible to test the level of agreement of EHT data with non-BH spacetime geometries (such as boson stars, wormholes, classical naked singularities, etc.) within GR, as well as both BH and non-BH spacetimes in non-GR theories (Völkel et al 2021;Kocherlakota et al 2021;The EHT Collaboration et al 2022b;Vagnozzi et al 2023). This program has seen intense activity, and current approaches use a combination of GRMHD simulations in Kerr BH spacetimes (see, e.g., The EHT Collaboration et al 2019bCollaboration et al , 2022b and non-GRMHD (xGRMHD) simulations in nonrotating spacetimes (Mizuno et al 2018;Olivares et al 2020;Fromm et al 2021;Röder et al 2023).…”